The invention relates to linear electric motors, and more particularly to such motors for downhole use in oil wells, and most particularly to such motors for operating sucker rod pumps in oil wells.
It has long been recognized that production of oil by means of sucker rod pumps driven by a surface mounted pumping jack, is very inefficient. Not only are the pumps and the sucker rod connecting the downhole pump to the pumping jack very expensive, but they also suffer from several technical problems.
One of the major problems is that, since most wells are not "straight", the sucker rod usually rubs against the tubing in a number of places. This problem is even more severe in wells that are intentionally directionally drilled and whose deviation from perfect straightness can be quite large. Not only does this wear the sucker rod and the tubing, necessitating the costly replacement of both, but the friction between the sucker rod and the tubing wastes energy and requires that more powerful motors be used to operate the pumping jack. In cases where the sucker rod completely wears through the tubing, there is also the problem of losing production from the production tubing back into the well casing. This rubbing action also causes the tubing to move up and down with the rods, necessiating the installation of tubing anchors.
Other problems associated with present sucker rod pumping systems are breakage of the bridle line connecting the pumping jack head to the polish rod, freezing of engine fluids in cold weather, pollution from engine exhaust, and leaks around the wellhead associated with the moving seal between the polish rod and the stuffing box.
Maintenance of sucker rod pumping systems is thus very costly not only in terms of replacement parts and labor but also in terms of lost production during the down time required for maintenance.
In addition to the technical problems associated with the prior art sucker rod pump systems, there are operational problems as well. Producing wells are usually scattered over a large geographic area, and the well owner must send a technician to each well on a regular basis to ensure that it is operating property, to adjust its operating characteristics to match the production pattern, to read gauges, etc. This operational pattern is both time consuming and costly. In low and marginal production wells, the problem is more severe since they require more constant attention to ensure that the pump operation accords with the abililty of the well to produce. For example, a pump on a marginal well must be constantly adjusted for maximum long term production and should be shut off when the well is temporarily pumped dry.
There are several types of information needed by reservoir engineers which can only be obtained under the current practice by shutting down the well and taking downhole measurements. One example is temperature which is an indicator of remaining formation production strength. New wells typically posssess a high bottom hole temperature, but the temperature drops as the well ages. In the current practice it is necessary to pull the pump in order to measure this parameter. Other important parameters include downhole pressure, which is useful in calculating reservoir volume, and fluid levels.
It is therefore the object of the present invention to provide a new and improved linear electric motor for driving a downhole sucker rod pump or other similar device, which overcomes the limitations and drawbacks of the prior art.